Body for land vehicles, especially railway cars, and method of its assembly



NOV. 25, 1952 DEAN 2,619,045

BODY FOR LAND VEHICLES, ESPECIALLY RAILWAY CARS, AND

METHOD OF ITS ASSEMBLY Filed July 14, 1948 4 Sheets-Sheet 1 INVENTOR. =Qlbert CLDecm;

MJMM

Npv. 25, 1952 Filed July 14, 1948 A G DEAN 2,619,045

BODY FOR LAND VEHICLES, ESPECIALLY RAILWAY CARS, AND

METHOD OF ITS ASSEMBLY 4 Sheds-Sheet 2 I 31 I T/R I NV' 30 LI W M I my I [I3 @1 I@ 'Q U g \I [U INVENTOR.

ATTORNEY A. G. DEAN 2,619,045 BODY FOR LAND VEHICLES, ESPECIALLY RAILWAY CARS, AND

Nov. 25, 1952 METHOD OF ITS ASSEMBLY 4 Sheets-Sheet 3 Filed July 14, 1948 INVENTOR.

. aqlberf CT. Dean BY A %W i.

I ATfORNEY A. G. DEAN BODY FOR LAND VEHICLES, ESPECIALLY RAILWAY CARS, AND METHOD OF ITS ASSEMBLY 4 Sheets-Sheet 4 Filed July 14, 1948 INVENTOR.

Albert 6. Dean, By m 4/ @w ATTORNEY PIC-1.9

Patented Nov. 25, 1952 BODY,ljFDR,-' IJAND .VEHICLES;.:ESPECIALLY t .RAILWAY CARS, AND sMETHOD OF ITS.

AS SEMBLY A Albert G. Dean; Narberth, -"Pa., assignor to-The Budd Gompany,- Philadelphia, Pa., a corpora- "tion o'f Pennsylvania Application July 14, 1948, Serial No." 38,128

I -14 Cla'ims.- (Cl."-105'399-) 1-. The 'invention relates to fthe construction ;of bodies "for land vehicles of long prismatic shape and j'comp'rising underframe, roof "and side wall structures. "Ihisjis ,theityp'e of body use'djoutstandingly for railway "cars of passenger trains,

but also used, although in shorter length, :for

fr'eigl'ithcars and highway "buss/es, trucks "and trailers.

More specifically, the inventionjrelatesito' bodies o'filithe "indicated type fl'iavirig an outer roof skin of thin gauge i sheet jimetal, which may The "corrugated longitudinally, "andfhavin'g a gently arched mid portion ofith'ei'i'oof adjoin'ed by more strongly arched side portions, the latterimerging into'.' the side Walls.

An outstanding object ofthe inventionflisjthe preventing or fminimizing 16f {the 'forma'tion of transverse waves or" buckles in thejr'oof skin which occur loutstandingly in'i the flat. or slightly arched top region or vthe "thin Jgauge roof "skin. Such waves or buckles .of the ro'ofjskin,v tending to'r'nar the appearance of theother'wise smooth Land straight." lines of an immaculate Imoidern: railway car, are ohservedmost vfrequently on hot "days whenra saris exposed. .to strong overhead sunlight. 'The causes of .such I waves, remained "ob; some for a long time, thereby barring .the 1di's-. covery of} effective countermeasures.

The present invention is based ,on the novel concept. that. difierentialjheating .of the roof, skin, on the one hand, and of other body parts, Onthe othelwhand, causes the more ,hig'hl'yheated'portions 'ofthe-roofslin, which have little resistance against mending ;or bukling, .to expand while sueh -vexpansion, is restrained by the other zless heated rand-consequently less expanded ,parts, thereby forcing the skin .tov :wave .or buckle, and the vinvention remedies this situation by liliolding the iroof skin, 1 preferably only itsgapproximately horizontal mid 1 portion, in longitudinal ,tension. A roof; skin tensioned in :this manner can 'not buckle on account of difierential heating unless and ,until thethermaliexpansiondifferentialsurpasses ,the -previquslengthening ofthe roof skin due. to .the tension imparted thereto.

The inventionalso-relates to a method of, assembling a body pf thelindicated type. Broadly speaking, this method consists in assembling the body so; thatthe, middle portion of the roof skin istensionedwhile otherelements are compressed. A specific form of this ,.method involves preassembling roof-.and side.wa11s sothat their-mating edges diverge vertically toward the ends of the body, and require bending the roof, in finalassemblyto make its margins conform to the side wall 2 inargins, thereby "imparting tension to "the "roof 'The above outlinedand' further. tob-j'ects; "ad vantages, features and thadetails -of =the inven= tion -will -b'e more fully-and more-easily understood from*theembodi-ments"of the-invention illustrated in the attached drawings and die scribed inthe-following.-

ln -the drawings;

Figure-1 is an-exploded"side elevatiohfa mu way "car TbOdy comprising" a preassembl'd'iroof unitand 'aunit including-the site wallsyeridwalis and 'underframe prior ,to "the ifinal- *assernbly *dt these unitsinto' the completedbody structure Figure 2 is-ra side elevation-of the "body" after the unitsas showniin' Figure "'1 have beenflinaliy assembled with "each: other;

"Figure 3"is :a' diagrammatic-section throughtthe body along line 3-13- of andon aylargerscale than Figure 2;;

Figure 4 is' a larger-scale fra'gmentaryperspec tive inside view of adjoining portions ofthe roof unit and one of-=-theside'wall units-"after their final "assembly Figure .5*is a perspective ViW ofthewside 'wall portion shownrin Figure 4 prior toits final=-as-' sembly with the roof unit;

Figure 6 is van exploded side elevation similar to but more diagrammatic andon asma-ller' scale thanFigure- 1, illustrating a= modifie'wmethodof assembling the body in accordance-with the -in-z ventiony Figure '7 is a fragmentarysectional i'per's'pective View; of a roof unit-With a smooth skinwhien'is outstandingly" susceptible- :to waves andcalls fo'r using the invention;

Figures is airagmentarysectional perspective view of one of the side wallstobe unitedwitl'rthe roof shown inFi'gure' 7 and Figure '9 is a diagrammatic longitudinal section" through part of theroofshown 'infFigureF'Z;

Following aicustomary procedurerthe railway car bodyfillustrated in-*Fi'gures l throu-gh 5 is built up "ofitheifollowing 'preasseinbledunits: an underframe; unitU, two sidewall units-"S; a' vestibule and a non=vestibule-end wall unit -'V and NV, the former combined-With end doonposts P; and a roof unit R The underframe unit U an'd the end-wall units "V and NV=ar merely diagrammatically indicated inthe drawingbecause their construction maybe of *known design. The u'nderframe unit may be preassembled -*with the'--side wall units S; the posts -P and -sometimes-the -end wall units 'V and into-a larger-'unit-towhieh the roof unit'R, is then added-in final' assemblys' Each side wall unit S comprises a plurality of longitudinally spaced vertical posts It! interconnected by a bottom sill or chord I, a window sill or chord I2, a window header or chord I3, dead light panels [4 between the window openings, and a shearpanel 15 between bottom sill l I and window sill |2.- The upper ends of the posts Ill of the side wall unit prior to their assembly to the roof project freely beyond the window header l3 and are provided on the inside with gusset plates IB constituting part of the final assembly means between the side wall unit and the roof unit. The end regions of each side wall unit are reinforced by vertically reinforced shear panels H.

The underframe structure U comprises a transversely reinforced shear panel l8, side sills l9 connected in final assembly with the sills ll of the side walls, and mostly comprises, in addition, a center sill, cross bearers and bolster beams which are not shown. The lines 20 indicate the location of the axis of the center plates on the bolster beams by which the body is carried on the trucks, likewise not shown.

The roof unit R comprises a continuous upwardly facing channel-section sleeper or chord structure 2| on each side, longitudinally spaced Z-section carlines 22 having their ends secured in the sleepers 21, a longitudinally corrugated roof skin 23 secured to the outer arms of the carlines 22, and on each side a downward extension of the roof skin, which may be in the form of a fiat letterboard 24, and the lower margin of which is reinforced by a molding 25. The roof is further reinforced by longitudinal purlines 26 secured to the carlines 22 and to the adjoining portions of the roof sheathing 23. The lateral edge portions 2'! of the roof are strongly arched and these portions merge without abrupt change of direction into the side walls and into the nearly horizontal, gently arched middle portion 28 of the roof.

As indicated in the drawings, the elements entering into the structure consistof sheet metal, preferably high tensile stainless steel, and are secured together by spot or seam welding, resulting in an integral self-supporting body structure.

In final assembly, the roof unit R is slid telescopingly over the side wall units S which, as indicated before, previously may have been united with the underframe, end wall and post units U, V, NV and P, whereupon the gussets IE on the'posts ID are secured by spot or plug welding to the inner wall of the roof chords 2|, and the skirts 24 of the roof unit together with the moldings 25 are secured to the outer flanges of posts and window headers I3 of the side wall units.

The construction and the assembly procedure described so far are substantially identical with the disclosure in applicants Patent No. 2,514,123, July 4, 1950. Certain features are also shown in the application Serial No. 38,726 of Gladeon M. Barnes, Charles L. Pike and the present inventor, entitled Roof for Land Vehicles, Especially Railway Cars, and Method of Making the Same, filed July 14, 1948, simultaneously with the present application.

The previously mentioned waviness of the roof skin or sheathing develops outstandingly in the approximately horizontal, gently arched mid region 28 and, more specifically, in about the central third of the length of the body. The occurrence of the waves or buckles in this restricted region is believed attributable to the combined influences of the above described differential thermal expansion and the compression of the roof due to the deformation of the body under the load supported by it, such deformation obviously being greatest halfway between the supports of the body at 20. The lateral. regions 21 of the roof sheathing are less apt to become wavy because of the stiffness derived from their arched cross-section and on account of the fact that they are less exposed to continuous overhead sunlight.

The invention reduces or suppresses the susceptibility to waves of the roof sheathing in the generally horizontal mid-roof region 28 by pretensioning the roof sheathing in this region, or at least the portion thereof near and adjacent the longitudinal center of the body. The extent of the region which is so pre-tensioned may be varied to fit the specific construction of the car body to which it is applied and the experience gained in regard to the limits of the region in which waviness may occur. Obviously, the desired result is achieved if the pretensioning is applied to a region larger than actually required.

One method of imparting the tensioning of the roof sheathing, which is illustrated in Figures 1 and 2, consists mainly in preassembling the side wall units or the side wall units with the underframe unit on the one hand, and the roof unit on the other hand, with different camber so that when the roof is superimposed on the side walls the mating margins of both types of units diverge from the longitudinal center toward the ends of the body.

As illustrated in Figure 1, the roof unit is assembled with the camber zero, that is: assembled with no camber at all, whereas the side wall units, with or without the underframe unit, are assembled so that the longitudinal mid region is higher than the end regions. The dot-anddash line 25 is a straight horizontal line paralleling the lower margins of the roof and showing the pronounced camber of the side wall units. Actually, the camber of the side wall units need not extend over the entire length of the car, but only over the mid portion thereof, such as over the portion between the supports at 20, whereas the outward regions may be straight. As will become apparent later on, this latter feature is in line with the above explained restriction of the occurrence of waves to the longitudinal mid region of the car.

In building the car, the following sequence of assembly operations is preferred: the roof and the side frames or walls are built to the desired camber in separate jigs; the side frames are then assembled with underframe and end walls on supports maintaining the camber; the roof unit is applied to the assembly consisting of side, ends and underframe, which assembly is still supported in maintaining the camber.

For finally connecting the roof unit U with the side walls S, the two are forced into continuous engagement with each other along their meeting margins, which means that the roof has to be bent down at the ends and/or the ends of the side walls have to be bent up. Such bending is well within the elastic limits of these structures. Whichever bending procedure is followed, after the roof is structurally united with the side walls and the body freed of the assembly fixtures or jigs, the roof ends will be held by the side walls in the downwardly bent form, causing the top portion of the roof to be held under tension, whereas a certain amount of compression aemgoau will -be imparted to "the downwardly projecting portionsof the roof. The roof unit "represents a downwardly facing channel-section girder or beam having a horizontal neutral plane above and'below which the longitudinal members of the roof are held under tension and compression respectively. The neutral plane in this construc tion isIlocated-above the bottom. level-of the sleepers approximately one-third the distance between said'level andthe'apex of the roof.

The tension under which the roof sheathing in thesr'egio'n'28 is held will effectively prevent the waviness of -.the sheathing which otherwise might be caused by thermal expansion alone or in combinationwith'the downward'bending of the'entirebody 'due to the load carried betweenits supports 20.

' The embodiment diagrammatically illustrated in Figure 6" difi'ers'from the first'emb'o'di'ment in that'the side walls S with or. without underframe "U, end walls NV, V and post P, are assembled :without cambe'n as indicated by the dote-and-dash line 36lrepre'senting the'topinarginiof-theside walls. The'roof unit R', on the otherhand, is assembled so that its-mid portion is lower than theend portions. The amount of the camber is revealed by comparison of. the roof with the straight horizontal dot-'and-dash line 31... Theresultof-forcing the mating margins of said -wall-units Sand roof unit R" into'engagementzwith'each other is substantially the same as that obtained by the construction and procedure 'accordingto Figures land 2.

For-'thetensioningof the roof skin by the difcssential'to'assemble roof and side walls so that their meeting margins diverge from th longitudinal mid region of the body toward the ends thereof, and it is not essential which of the two types of units has its margins curved or cambered, or whether the margins of both types of units are curved to a different degree. Nor is it necessary that the entire respective unit or uni-ts have the camber. 'For practical reasons, however, it appears recommendable to impart a camber; at least to the side wallunits because such camber is also, for other reasons, customarily mparted to a l ar v -It-is-alsoconsidered desirable to selectthe conditions so that the completed body structure retains a specified amountof camber which will be straightened out under the loadoi the equipment attached to the mid portion of the car. Thisfto o, isin line with customary practice.

Fro rn thseexplanations, it follows that the emb'od'imntillustrated in Figure 6 represents an extreme "case which, 'althc'ugh unlikely 'to be assisted in practice, "will clarify the extent to which 'thernethod'per Figures 1 and'2 'may'be modified.

For a railway car "of the construction illustrat'ed'in Figures 1 to 6,a difference of camber between the'mat ing margins of the side walls'and roof "amounting to for a distance of '59 6" betweenlthesupports'at 20, is considered adedilate. For a'total length of the same body of about"85', this involvesfa'total diiference or camber o fapproximately 1.5". In the drawings, the amount of. thecam'ber is exaggerated. The full understanding of the invention may be facilitated by giving some further dimensions 'of parts which influence the result. As examplesthe following are dimensionsdesigned to be used in the body illustratedlin Figures 1 to 5 or in Figure 6:

gauge ofthe roof skin .02" radius of transversecurvature o'f :the marginal portions 21 0f the roer skin, about 20"; radius of transverse curvature of the central portion 28 of roof skin, about 10' to 11'; gauge of roof sleepers and carlines .06"; spacing of-carli'nes, about 27.5; width of body, about 10'; gauge of letterboard .09; and-height of side walls, about 7.5

The invention is, perhaps with even greater benefit, applicable to constructions having a smooth roof skin which is more subject to waviness than a skin stiffened :to some: extent by corrugations. "Furthermore, the invention is notrestrictedto'a roof unit comprising a'skirt or letterboard which 9 extends downwardlybeyond the lateral roof chords. -A'construction in which the roof skin terminates at'the lateral chords is more easily bendable than. a, roof chaving downwardly depending skirts or letterboards to be -held in compression which, unless special precautionsare taken, might lead to waviness of these skirts.

'A construction having a smooth roof surface and the letterboarcls on the sidewalls is illustrated in Figures 7 to 9. The r'oor-sheathing'or skin is composed of transverse strips32 which may be formed of coil stock approximately 27" wide and having one edge joggled at 33. In a special fixture, each of these sheets 32 is welded at wide intervals by its joggled'margin 33 to one of the carlines 3d, resulting in subassemblies, each consisting of one w sheet and one carline, which are then placed progressively in thesleeper channels 35 so that each unit maybe-welded to the previously installed-units by means of a reasonably short-throated toolor multiple-electrode special set-up reaching in through theend. In addition, two purlines (not shown) maybe :used at the same location as that illustratedin -Figure 3,. and possibly a furtherpurline along the center line, indicated by the dot-and-dash line 36 in FigureQ. The'sleepers and the purlines may be welded to each subassembly unit as it is installed, thereby completing the roof unit R".

Each side wall unit S" includes vertical posts 3? which are interconnected by dead light panels 38 and by chord structures and sills (not shown) in a manner similar to that shown for the construction of Figures 1 to 5. However, the side wall units of this embodiment differ from the first embodiment in that they include the letterboard 39 and the header molding 40. The letterboard may have a gauge of .09 and the roof sheets a gauge of .05" to .06". The material of both these elements and of most of the other elementsentering into the construction is preferabiy high tensile material, for instance, cold rolled austenitic stainless steel.

In order to help keep the roof skin flat in the car, the top portion of the skin is held in tension. Similarly to the procedure described for the previous embodiments, the roof may be built to less camber than the car, and possibly even reverse camber. When the roof is pulled to the camber of the side frames in the final assembly, the roof is bent about its horizontal neutral plane, and this will tend to stretch the sheets tight in the upper portion where curvature is least and buckles are most like to occur. 'In this construction, the neutral plane is located above the bottom level of the sleepers at approximately the distance between said level and the apex of the roof.

The connection between roof and side walls may be strengthened by a web lLJindicated by, dot-and-dashlines in Figure 8,.awhich'is secured ,7 to-the "posts" 31, and sleepers 35 and the carlines In addition to the illustrated and described embodiments, the invention is susceptible to many further modifications and to adaptations to different body constructions. It is important to understand that the procedures for tensioning the roof skin illustrated and described in this application may be modified or replaced by other procedures which, in the knowledge of the condition to be imparted to the roof skin in accordance with the invention, present themselves to those skilled in the art. In short, protection is sought for the broad aspects of the invention in addition to protection for combinations including specific features of the body construction and independently of any specific methods by which the inventive condition of the roof skin is attained.

What is claimed is:

i. In a railway car body for passenger trains, comprising side Walls and a transversely arched roof, the roof including longitudinally spaced transverse carlines secured at their ends to the side walls and a thin roof sheathing secured to the carlines, the marginal portions of the roof and the side wallspresenting vertically disposed beams of appreciable extent and bending moment, said roof sheathing at least in part being held under longitudinal tension by said marginal portions and side walls so as to avoid waviness of the roof sheathing especially when exposed to strong overhead sunlight causing thermal expansion of the sheathing.

2. In a railway car body for passenger trains in the form of a long prismatic body having a transversely arched roof, the body including longitudinally extending frame structures of considerable vertical extent adapted to withstand compression loads without buckling and a roof skin of thin sheet metal supported by and secured to longitudinally spaced transverse carlines, the approximately horizontal mid region of the roof skin being held under tension by said longitudinal frame structures to counteract the tendency to the formation of waves and buckles in said mid region of the roof skin.

3. In a terrestrial closed vehicle body of elongated prismatic form, such as a railway car body for passenger trains, having longitudinally extending side walls and a transversely arched roof said side walls having greater resistance against bending in vertical direction than the roof; said roof comprising lateral longitudinally extending chord structures, longitudinally spaced transversely extending carlines secured by their ends to said chordstructures, and a sheet metal roof sheathing secured to the outside of said chord structures and carlines; the marginal portions of the roof and the side walls presenting vertically disposed beams of appreciable extent and bending moment; the gauge of said roof sheathing being so small as to render it susceptible to the formation of waves, especially when exposed to strong overhead sunlight; in the completed body, said roof structure being held in a condition in which its ends are bent downwardly by said side walls thereby imparting tension to the mid region of the roof skin between its lateral sides and counteracting the susceptibility to the formation of waves.

.4. In a terrestrial closed vehicle body of elongated pri'smatic form, such as a railway car body for passenger trains, having longitudinally extending side walls merging without abrupt change of direction into the sides of a transversely arched roof; said side walls having great resistance against compression in longitudinal direction and against bending in vertical direction; said roof comprising lateral longitudinally extending chord structures, longitudinally spaced transversely extending carlines secured by their ends to said chord structures, and a roof sheathing of longitudinally corrugated sheet metal secured to the outside of said chord structures and carlines; the gauge of the roof sheathing being so small as to render it susceptible to the formation of waves; in the completed car body said roof structure being held in a state in which its ends are bent downwardly thereby imparting tension to the mid region of the roof skin between its lateral sides and counteracting said susceptibility to the formation of waves.

5. In a terrestrial closed vehicle body of elongated prismatic form, such as a railway car body for passenger trains, having longitudinally extending side walls interconnected at the top by a roof, said roof having arched side portions merging without abrupt change of curvature into the side walls and into the less arched approximately horizontal mid portion of the roof, said roof comprising an outer sheathing of Iongitudinally corrugated thin sheet metal; the marginal portions of the roof and the side walls presenting vertically disposed beams of appreciable extent and bending moment; said sheathing in said approximately horizontal mid portion of the roof being held under tension in longitudinal direction by its connection to said side walls so as to counteract the tendency to formation of waves in this region of the roof.

6. In a closed land vehicle body forming an elongated prismatic hollow beam of the type used for railway cars, busses, trucks and trailers, and having side walls, strongly arched portions along the upper longitudinal margins of the body merging into the side walls and into a gently curved portion of the roof interconnecting said strongly arched corner portions, said gently curved roof portion having a thin gauge sheet metal skin held, at least in the longitudinal mid section of the body, under longitudinal tension by adjoining longitudinally extending elements of the body.

7. In a closed land vehicle body of elongated prismatic form of the type used for railway cars, busses, trucks and trailers, having side walls and a transversely arched roof merging by its lateral portions into the side Walls without abrupt change of direction, longitudinally extending sleepers in the regions where roof and side walls meet, longitudinally spaced transverse carlines interconnecting the sleepers and a thin gauge roof sheathing secured to the outside of the carlines, the body including a roof unit preassembled independently of the preassembled side walls, the sidewalls and the roof unit being preassembled so that prior to the connection between side walls and roof unit their mating margins diverge vertically in longitudinal direction from the longitudinal mid region of the body toward the end regions, the top portion of the roof sheathing being in the state of tension in the finished body due to the forcing together of the diverging margins of side walls and roof and the ensuing bending of the roof.

8. In a closed land vehicle body of elongated prismatic form of the type used for railway cars,

busses, trucks and trailers, having side walls and a transversely arched roof, the latter merging by its lateral portions into the side walls without abrupt change of direction, longitudinally extending sleepers in the regions where roof and side walls meet, longitudinally spaced transverse carlines interconnecting the sleepers and a thin gauge roof sheathing secured to the outside of the carlines, the marginal portions of the roof and the side walls presenting vertically disposed beams of appreciable extent and bending moment, the body being assembled so that the roof is held in a condition in which portions thereof remote from the longitudinal middle of the body are held in downwardly bent state, thereby holding the top portion of the roof sheathing in tens1on.

9. In a transversely arched roof for land vehicle bodies, especially railway car bodies of passenger trains, longitudinally extending structural members adapted to withstand compression loads Without buckling, and a roof skin of thin sheet metal supported by and secured to longitudinally spaced transverse carlines, the longitudinal mid region only of the roof skin being held under tension by compression of said longitudinal structural members.

10. In a method of building elongated prismatic land vehicle bodies of the type used for passenger railway trains and having a transversely arched roof with a thin roof sheathing, compressing longitudinal structural members of the body near the top thereof while assembling the body, and letting such compression react against the sheathing at the top of the roof so that this part of the sheathing is tensioned for straightening it and, for preventing the formation of waves and buckles therein due to heat expansion and other causes.

11. In a method of building elongated prismatic land vehicle bodies of the type used for passenger railway trains and having a thin roof sheathing, the step of preassembling a roof unit independently of the side walls so that the top margins of the side walls and the mating lateral margins of the roof unit differ in camber and diverge toward the ends of the body, and the step of securing the mating margins of side walls and roof unit together while bending the ends of the roof downwardly, whereby the roof sheathing above the neutral plane of the roof unit is tensioned so as to prevent the formation of waves in the roof sheathing due to heat expansion and other causes.

12. In a method of building elongated prismatic land vehicle bodies of the type used for passenger railway trains and having a thin roof sheathing, the step of preassembling a roof unit independently of the side walls so that the top margins of the side walls and the mating lateral margins of the roof unit differ in camber and diverge toward the ends of the body, the step of preassembling the side walls with the underframe into one unit prior to the assembly of this combined unit with the roof unit, and the step of securing the mating margins of side walls and roof unit together in bending the ends of the roof downwardly, whereby the roof sheathing above the neutral plane of the roof unit is tensioned so as to prevent the formation of waves in the roof sheathing due to heat expansion and other causes.

13. In a method of building elongated prismatic land vehicle bodies of the type used for passenger railway trains and having a transversely arched roof with a structural sheet metal skin, the step of independently preassembling side wall units and a roof unit so that the side wall units and the roof unit differ in camber and, when superimposed preparatory to their connection, have their mating margins diverging from the middle toward the ends of the body, and the step of securing the mating margins of side wall units and roof unit together while bending the ends of the roof downwardly and causing the roof sheathing above the neutral plane of the roof structure to be tensioned.

14. In a method of building elongated prismatic land vehicle bodies of the type used for passenger railway trains and having a transveresly arched roof with a structural sheet metal skin, the step of independently preassembling side wall units and a roof unit so that the side wall units and the roof unit differ in camber and, when superimposed preparatory to their connection, have their mating margins diverging from the middle toward the ends of the body, the step of connecting the side wall units, prior to their assembly with the roof unit, with a preassembled underframe unit while maintaining the camber, and the step of securing the mating margins of side wall units and roof unit together while bending the ends of the roof downwardly and causing the roof sheathing above the neutral plane of the roof structure to be tensioned.

ALBERT G. DEAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,770,932 Leake July 22, 1930 1,770,933 Leake July 22, 1930 2,017,629 Lindsay Oct. 15, 1935 2,314,978 Gunn Mar. 30, 1943 2,314,979 Gunn Mar. 30, 1943 2,342,025 Watter Feb. 15, 1944 2,405,793 Lohse Aug. 13, 1946 

